The combination of genetic susceptibility and environmental exposure is suspected of contributing significantly to the occurrence of common human congenital malformations. Folic acid use early in pregnancy reduces the risk of conotruncal heart malformations, but the mechanism underlying this reduction is unknown. On the basis of epidemiologic and experimental evidence, two unifying hypotheses have emerged. First, we hypothesize that folate insufficiency may have a direct teratogenic effect on cells that utilize folate-specific binding and transport proteins. Second, we hypothesize that maternal hyperhomocysteine inhibits the function of the N-methyl-D-aspartate type of glutamate (NMDA) receptor, and that homocysteine may interact with other teratogens that also inhibit NMDA receptor function. The overall goal of this project is to test each of these hypotheses by integrating epidemiologic data (3000 cases and controls) with the measurement of human genetic variation by polymerase chain reaction-based genotyping. There are 3 specific aims of this project: Aim 1: to analyze whether genetic variations of maternal or infant folate- pathway genes modify risk of conotruncal malformations, in the presence of variations in maternal folate intake. Aim 2: to analyze whether women exposed to NMDA receptor antagonists are at increased risk of delivering infant or fetuses with conotruncal malformation; and whether this effect is exacerbated with low maternal folate or abnormal folate metabolism, providing a key test of the second hypothesis. Aim 3: to analyze if women who consume higher or lower levels of selected nutrients are at increased risk of delivering offspring with conotruncal malformations, addressing the paucity of information about the interrelations among folate, homocysteine and other nutrients on early heart development. Understanding the mechanisms by which nutrition, genetic background and environmental exposures interact will substantially increase the probability of developmental malformations.